1. Field of the Invention
The present invention relates to a method 1 for controlling a fluid compression system. The invention also concerns a control system suited for controlling a fluid compression system.
2. Description of the Prior Art
In conventional compression systems of a fluid medium, particularly compressed-air systems, the outlet pressure of the compressor is sensed, and this information is used to control the compressor operation with the help of a pressostat placed immediately at the compressor outlet. In compressor models equipped with a no-load unloading facility, the duration of the unloaded no-load running mode can be controlled by an adjustable timer. The set time is always constant until changed manually. Such control schemes are not capable of taking into account pressure losses caused by air consuming equipment attached to the system and variations in compressed air demand. Pressure loss occurring in the equipment is entirely dependent on instantaneous air flow rate and pressure. These variables may change by a large amount within a short interval of time. Moreover, the pressure loss caused by filters on the compressed-air line is dependent on the degree of clogging of the filters. When new, the filter causes a small pressure loss which increases with the clogging of the filter when it binds impurities from the through-flowing air. When sufficiently clogged, the filter element is replaced, whereby the pressure loss is again reduced to a low level.
To the user of the compressed-air system, it is extremely important that proper pressure level for the compressed-air operated equipment is ensured at the point of demand.
A disadvantage of prior-art equipment is that they require the compressor working pressure to be set to an unnecessarily high level due to the incapability of such equipment to compensate for the pressure losses caused by the above-mentioned accessories or devices. Resultingly, the energy consumption of the compressed-air system is unnecessarily high. Moreover, for compressors operated with period of unloaded postrunning mode, the duration of the postrunning mode is set according to the rule that the frequency of compressor starts may not exceed the maximum frequency of starts specified for the drive motor. This duration of the postrunning mode is fixed and unrelated to variations in compressed-air demand, thus permitting the compressor to run unloaded for the preset duration of the postrunning mode even during times of no compressed air demand. In this case, unnecessary energy losses occur.
Also in conjunction with compressed-air systems having two or more compressors, control systems based on conventional techniques cause superfluous energy consumption. Very commonly a pressure swing of small amplitude or short duration starts the second or the other compressors even when no extra air would actually be required. Further, if the compressor is operated using an unloaded no-load running mode, the proportion of useless energy consumption may rise up to about 40% of the nominal electrical input rating of the compressor yet producing no air to the compressed-air network.
Energy consumption in conventional compressed-air systems is on the average more than 30% greater than the theoretical minimum due to the following reasons:
To fulfill the pressure requirements of the user equipment under varying conditions of air demand, the compressor working pressure must be set significantly higher than the average pressure demand; PA1 The compressor operating control system by no means takes into account the effect of the amount of air demand and the degree of filter contamination on pressure losses occurring in the compressed-air circuit; PA1 The duration of the postrunning mode of the compressor intended to protect the drive motor is constant, thus failing to adjust the actually needed duration of the postrunning mode according to the variations in air demand; and PA1 Multiple compressor systems are unnecessarily sensitive, and entirely useless compressor starts are triggered which are caused by the delay from the compressor start to the instant of effective compressed air production.